Engineers have long known that combustion efficiency, exhaust emissions and noise in a diesel type internal combustion engine can be improved by controlling the injection rate of fuel to the combustion chamber. Over the years, engineers have identified at least four different injection rate shapes that decrease undesirable emissions and noise from an engine, depending upon the engine's particular operating conditions. These four different injection rate shapes are generally known in the art as a square, ramp, boot and pilot injection rate shapes. These different injection rate shapes generally refer to the front end portion of the injection rate profile. In almost all cases it is desirable that the injection rate provide a nearly vertical abrupt end to each injection event. While there are many fuel injectors that have the ability to provide at least one of the desired injection rate shapes, engineers have encountered substantial difficulty in providing a single fuel injector or fuel injection system that can provide each of the different injection rate shapes on command during a given operating condition for an engine. In other words, the ability to control the injection rate at each point during an injection event has proved very problematic to achieve.
The present invention is directed to overcoming one or more of the problems as set forth above.